Re: [PATCH v3 2/2] sysdeps/clock_gettime: Use clock_gettime64 if avaliable

[Alistair Francis <alistair23 at gmail dot com>]

 isOn Tue, Dec 3, 2019 at 11:29 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 23/11/2019 19:27, Alistair Francis wrote:
> > With the clock_gettime64 call we prefer to use vDSO. There is no call
> > to clock_gettime64 on glibc with older headers and kernel 5.1+ if it
> > doesn't support vDSO.
>
> Ok with the fix below regarding HAVE_CLOCK_GETTIME64_VSYSCALL.

Thanks for the review.

>
> > ---
> > This was patch was runtime tested with RV32 and RV64
> > It was build tested using the ./scripts/build-many-glibcs.py script.
> >
> > I also ran:
> > $ make ; make install ; make check
> > tests on native ARM (32-bit) with the following three confiugrations:
> >  - 4.19 Kernel and 4.19 Headers
> >  - 5.2 Kernel and 4.19 Headers
> >  - 5.2 Kernel and 5.2 Headers
> > and didn't see any regressions
> >
> > v3:
> >  - Assume HAVE_CLOCK_GETTIME64_VSYSCALL means we have __NR_clock_gettime64
> >  - Change code style to be more glibc-ish
> > v2:
> >  - Add commit message
> >  - Change ret_64 to int
> >
> >  include/time.h                          |  3 ++
> >  sysdeps/unix/sysv/linux/clock_gettime.c | 44 ++++++++++++++++++++++++-
> >  2 files changed, 46 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/time.h b/include/time.h
> > index d7800eb30f..c19c73ae09 100644
> > --- a/include/time.h
> > +++ b/include/time.h
> > @@ -211,11 +211,14 @@ extern double __difftime (time_t time1, time_t time0);
> >
> >  #if __TIMESIZE == 64
> >  # define __clock_nanosleep_time64 __clock_nanosleep
> > +# define __clock_gettime64 __clock_gettime
> >  #else
> >  extern int __clock_nanosleep_time64 (clockid_t clock_id,
> >                                       int flags, const struct __timespec64 *req,
> >                                       struct __timespec64 *rem);
> >  libc_hidden_proto (__clock_nanosleep_time64)
> > +extern int __clock_gettime64 (clockid_t clock_id, struct __timespec64 *tp);
> > +libc_hidden_proto (__clock_gettime64)
> >  #endif
> >
> >  /* Use in the clock_* functions.  Size of the field representing the
> > diff --git a/sysdeps/unix/sysv/linux/clock_gettime.c b/sysdeps/unix/sysv/linux/clock_gettime.c
> > index ca40983f6c..875c4fe905 100644
> > --- a/sysdeps/unix/sysv/linux/clock_gettime.c
> > +++ b/sysdeps/unix/sysv/linux/clock_gettime.c
> > @@ -17,6 +17,7 @@
> >     <https://www.gnu.org/licenses/>.  */
> >
> >  #include <sysdep.h>
> > +#include <kernel-features.h>
> >  #include <errno.h>
> >  #include <time.h>
> >  #include "kernel-posix-cpu-timers.h"
> > @@ -30,10 +31,51 @@
> >
> >  /* Get current value of CLOCK and store it in TP.  */
> >  int
> > +__clock_gettime64 (clockid_t clock_id, struct __timespec64 *tp)
> > +{
> > +#ifdef __ASSUME_TIME64_SYSCALLS
> > +# ifndef __NR_clock_gettime64
> > +#  define __NR_clock_gettime64   __NR_clock_gettime
> > +#  define __vdso_clock_gettime64 __vdso_clock_gettime
> > +# endif
> > +   return INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp);
>
> Ok, in this case either __vdso_clock_gettime/__NR_clock_gettime or
> __vdso_clock_gettime64/__NR_clock_gettime64 will be called.
>
> > +#else
> > +# if defined HAVE_CLOCK_GETTIME64_VSYSCALL
> > +  int ret64 = INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp);
> > +  if (ret64 == 0 || errno != ENOSYS)
> > +    return ret64;
> > +# endif
> This should be:
>
> #if defined __NR_clock_gettime64
>   int ret64 = INLINE_VSYSCALL (clock_gettime64, ...)
>   [...]

This doesn't work for 32-bit archs. As HAVE_CLOCK_GETTIME_VSYSCALL is
defined, HAVE_VSYSCALL is also defined, but we then use the #if
defined __NR_clock_gettime64 clause and fail to compile as there is no
VDSO for gettime64.

This diff works

diff --git a/sysdeps/unix/sysv/linux/clock_gettime.c
b/sysdeps/unix/sysv/linux/clock_gettime.c
index 5051a87f83..575590475c 100644
--- a/sysdeps/unix/sysv/linux/clock_gettime.c
+++ b/sysdeps/unix/sysv/linux/clock_gettime.c
@@ -22,7 +22,9 @@
 #include <time.h>
 #include "kernel-posix-cpu-timers.h"

-#if defined HAVE_CLOCK_GETTIME_VSYSCALL || defined
HAVE_CLOCK_GETTIME64_VSYSCALL
+#if defined __ASSUME_TIME64_SYSCALLS
+  || (defined HAVE_CLOCK_GETTIME_VSYSCALL && !defined __NR_clock_gettime64)
+  || (defined HAVE_CLOCK_GETTIME64_VSYSCALL && defined __NR_clock_gettime64)
 # define HAVE_VSYSCALL
 #endif
 #include <sysdep-vdso.h>

Otherwise we can't use #if defined __NR_clock_gettime64

>
> And before sysdep-vdso.h it should be.
>
> #if defined HAVE_CLOCK_GETTIME_VSYSCALL || defined HAVE_CLOCK_GETTIME64_VSYSCALL
> # define HAVE_SYSCALL

I'm assuming you mean # define HAVE_VSYSCALL

Alistair

> #endif
>
> If !HAVE_SYSCALL the INLINE_VSYSCALL is defined as INLINE_SYCALL.
> It means that if an architecture does provide __NR_clock_gettime64
> but not provide HAVE_CLOCK_GETTIME64_VSYSCALL, it will still use
> the syscall. This code only uses the syscall if the vDSO is still
> present.
>
> I hope I can get my vDSO refactor, which would simplify a bit this
> code.
>
> > +  struct timespec tp32;
> > +  int ret = INLINE_VSYSCALL (clock_gettime, 2, clock_id, &tp32);
> > +  if (ret == 0)
> > +    *tp = valid_timespec_to_timespec64 (tp32);
> > +  return ret;
> > +#endif
> > +}
>
> Ok, old fallback to time32 vdso/syscall.
>
> > +
> > +#if __TIMESIZE != 64
> > +int
> >  __clock_gettime (clockid_t clock_id, struct timespec *tp)
> >  {
> > -  return INLINE_VSYSCALL (clock_gettime, 2, clock_id, tp);
> > +  int ret;
> > +  struct __timespec64 tp64;
> > +
> > +  ret = __clock_gettime64 (clock_id, &tp64);
> > +
> > +  if (ret == 0)
> > +    {
> > +      if (! in_time_t_range (tp64.tv_sec))
> > +        {
> > +          __set_errno (EOVERFLOW);
> > +          return -1;
> > +        }
> > +
> > +      *tp = valid_timespec64_to_timespec (tp64);
> > +    }
> > +
> > +  return ret;
> >  }
> > +#endif
> >  libc_hidden_def (__clock_gettime)
> >
> >  versioned_symbol (libc, __clock_gettime, clock_gettime, GLIBC_2_17);
> >
>
> Ok.